Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
CMOS image sensors are sometimes regarded the first three dimensional semiconductor devices in volume manufacturing. Chip stacking was integrated into fabrication procedures with the advent of backside illuminated image sensors, which involve reversing the structural order of the circuitry, lenses, and photodiodes from traditional frontside illuminated devices. Many backside illuminated devices require attaching the photoactive chip (i.e., the chip with photodiodes) to a logic wafer. This may be accomplished by flipping the photoactive chip, thinning the backside of the chip, and bonding the frontside of the chip to a readout layer using a direct oxide bond. Through-silicon-vias are often used as interconnects around the perimeter of backside illuminated devices.
However, with increased complexity of device architecture comes increased fabrication time and cost. Additional process steps may drive up production expenses and lower profit margins.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.